The present invention relates to an automobile radio telephone apparatus capable of detecting a drop of power source voltage thereof and, more particularly, to an automobile radio telephone apparatus of the type informing, when a power source voltage thereof is lower than a predetermined voltage, the user of the apparatus of such a voltage drop and, on the lapse of a predetermined period of time and if a conversation is under way, warns the user that it will execute a forcible conversation ending procedure and then executes it This type of apparatus is successful in preventing a telephone channel from being occupied wastefully over a substantial period of time and thereby enhancing efficient use of channels available with the entire automobile radio telephone system.
An automobile radio telephone apparatus belongs to a family of mobile radio communication apparatuses extensively used today. It has been customary to construct an automobile radio communication apparatus such that when the output voltage of a battery drops below a predetermined voltage, an alarm tone is produced through a handset and/or an alarm is indicated on a display to alert the user to such an occurrence. This type of conventional apparatus allows the user to continuously hold a conversation despite the alarm tone or the alarm display, until the user ends it intentionally. Then, the battery voltage will in due course become lower than the operable voltage of the apparatus, causing the apparatus to be reset. When the apparatus is reset, it stops transmission and thereby ends the conversation halfway. However, a base station to which the apparatus is connected holds the channel several more seconds and then releases it, since the apparatus does not send an end-of-communication signal thereto. For such several seconds, therefore, the apparatus occupies the channel simply wastefully and thereby prevents channels of the entire automobile telephone system from being used efficiently.